Easy mode: Alien Invasion. An alien invasion would quickly render the marxists and world financial powers meaningless, uniting the race to fight back or die.

Normal mode: Zombie Apocalypse. They are simply the undead, and the undead can be tricked. And even if the dead outnumber the living, you can still survive if you're smart about it

Hard mode: A leftist totalitarian world government is a difficult enemy that seeks to control everything. However, they can be fought back against - and without american taxpayer dollars funding them, their powers rapidly collapse. The fight's gonna be a lot harder, though.

Lunatic mode: Nuclear Armageddon. Unless you were well-prepared ahead of time with a budget of a few billion dollars, and willing to live deep underground for years, you're a goner.